The present invention relates to a friction stir welding method. Especially, it relates to a welding method appropriate for manufacturing the body of a car that runs on rails, such as a railway car.
Friction stir welding method is a method for bonding members by inserting a round shaft (called a rotary tool) to a joint portion and moving the tool along the joint line while rotating the tool, so as to heat, soften and plasticize the joint portion thereby performing solid-phase bonding of the members. The rotary tool comprises a large-diameter portion and a small-diameter portion. The small-diameter portion is inserted to the members to be bonded, and the end surface of the large-diameter portion comes into contact with the members. The small-diameter portion is provided with a screw. Moreover, a protrusion is formed to the butted portion of the two members to be bonded together, and the rotary tool is inserted from the side provided with this protrusion so that the metal constituting the protrusion fills the gap between the two members. The large-diameter portion of the rotary tool is inserted to the protrusion. When friction stir welding hollow members, the connecting plate that connects two face plates is used as the supporting board when friction stir welding the hollow members together. These methods are disclosed for example in Japanese Patent Publication No.3070735 (U.S. Pat. No. 6,050,474) and Japanese Patent Laid-Open Publication No. 2000-334581 (EP1055478A1).
Moreover, Japanese Patent Laid-Open Publication No. 2000-233285 discloses in FIG. 14 a method for friction stir welding two members while positioning a filling member in the gap formed between the two members. Furthermore, Japanese Patent Laid-Open Publication No. 2000-167677 (EP0992314A2) discloses a friction stir welding method for welding a first member having a protrusion with a second member not having a protrusion, wherein intermittent buildup welding is performed to the second member before performing the friction stir welding.
When a gap exists between the two members to be welded, it is very difficult to perform friction stir welding. Therefore, a protrusion is formed to the surface of the member where the rotary tool is to be inserted, so as to fill the gap with the metal constituting the protrusion. However, in reality when the gap exceeds 1 mm for example, it is difficult to obtain a good joint. It may be possible to increase the diameter of the rotary tool as the gap widens, but this may cause other inconveniences.
The car body of a railway car and the like that runs on rails include side structures that constitute the inner side surfaces of the vehicle, a roof structure, and an underframe that forms the floor. The first step for manufacturing a car body is to manufacture the side structures, the roof structure, and the underframe, respectively, by bonding plural extruded members. Next, these structures are bonded to form the car body. The size of each side structure, roof structure and underframe is approximately 20 m in length and 3 m in width, so there is a possibility of a large fabrication error. This error causes the gap of the joint portion to easily exceed 1 mm. The object of the present invention therefore is to obtain a good weld even when a large gap exists.
The second object of the present invention is to provide a simple friction stir welding method for bonding the underframe and the side structures of the car body, and for bonding the side structures and the roof structure thereof.
The objects mentioned above are achieved by positioning a member for filling the gap to the gap existing in the butted portion between two members, and then performing friction stir welding thereto.
Moreover, the member for filling the gap can be arranged in a gap formed by cutting the butted portion of the two members.
Even further, the butted portion of the two members can be cut and the two members can be moved closer together before performing friction stir welding thereto.
As for the second object of providing a simple friction stir welding method for welding the underframe and the side structures, either the surface plate of the underframe is used as supporting means, or a supporting device is arranged between two side structures, thereby facilitating the process.
The friction stir welding of the side structures and the roof structure is facilitated by providing a support device between the two side structures.